Previously, in the solid-state imaging device, electric charge present in a light receiving unit has been detected as electric current (hereafter, described as “dark current”), whether or not light is incident on the light receiving unit which carries out a photoelectric conversion of the incident light. As a result, the conventional solid-state imaging device has a problem that it perceives that an image brighter than the actual one is present.
To solve this problem, it has been proposed to form a fixed charge layer above the light receiving unit. For example, if negative electric charge is generated due to photoelectric conversion, the fixed charge layer is configured to attain the negative electric charges. In such a solid-state imaging device, the positive electric charges in the light receiving unit are accumulated at the upper surface of the light receiving unit, because the negative electric charge in the fixed charge layer attracts the positive electric charge. The accumulation results in recombination of the negative electric charge present in the light receiving unit with the positive electric charge accumulated at the upper surface of the light receiving unit, regardless of the presence of incident light. Thus, it is not likely that the negative electric charge present in the light receiving unit is detected as the dark current. Therefore, by having the fixed charge layer, the solid-state imaging device can control or prevent the generation of dark current.
To the contrary, if the electric charges generated by the photoelectric conversion are positive, a fixed charge layer having a positive electric charge is formed above the light receiving unit. By the fixed charge layer, generation of dark current can be similarly controlled or eliminated.
However, to control the generation of dark current more reliably, it is necessary to further increase the amount of electric charges held in the fixed charge layer.